Germans did indeed go to French restaurants, theaters, parties, etc.

There was a LOT more collaboration going on in France than people are generally led to believe. French police rounded up Jews for deportation to death camps. Thousands of Frenchmen served in the SS in combat on the Eastern Front. French women of both high and low economic class had relations with Germans, plenty of them quite willingly. You may have heard of Coco Chanel before - her boyfriend during the war was in the Abwehr (German spy agency) and there are documents claiming she worked with them too. Other famous 'high class' collaborators include Louis Vuitton and Pierre Benoit, among plenty others.

There were many organizations and individuals that collaborated at both high and lower 'classes' of life - it would not be unusual at all to see German soldiers in a fancy restaurant. Indeed, due to rationing issues it was likely that German officers were more likely to be able to afford to than the average French citizen under ever increasing rationing.

You may forget that for the most part, France was NOT an active warzone in between the initial blitzkrieg and the Normandy invasion. The Vichy Government of France collaborated with the Germans and peace was largely kept - there were of course all sorts of incidents but certainly not comparable to what was happening in the East. There was not widespread guerilla warfare. German troops were not really allowed to just go on wild random massacres in the guise of 'clearing communists' like they could in the East. A more "unrealistic" scene in Inglourious Basterds is when the Jew Hunter just shoots up the farmhouse in the beginning of the movie, killing all the Jews hiding under the floor. France was not considered a place where the Germans could just massacre Jewish children openly in front of witnesses - they were most often deported, and the roundups were usually done by French police or "Milice", a right-wing organization.

People collaborated for many different reasons. Some were economic opportunists. Some were actual Nazis. Some believed the war was lost and France would heal quicker by just getting on with the new order. Some were anti-communists, and who is killing more communists than the Nazis? Some were just young girls who do what young people do - especially considering the fact that millions of young Frenchmen were POWs or working as forced labor in Germany. Many collaborators were just making the best of a shitty situation. After the Allied troops came through many thousands of collaborators were executed, beaten, whipped, and in the case of women often stripped and had their heads shaven while being paraded around town to a gauntlet of beatings and insults. Many of the people dispensing this 'justice' were collaborators on some level themselves, eager to show how 'patriotic' they are by beating up teenaged girls now that the Allies had won. Needless to say, the situation was complex.